The present invention relates generally to laser beam delivery systems. More specifically, the invention relates to devices, systems and methods for homogenizing a laser beam for use in refractive surgery.
Laser beam delivery systems designed to improve the temporal and spatial characteristics of collimated beams of radiation with non-symmetrical energy profile cross sections are known. Some systems, for example, are used to deliver excimer laser beams for performing refractive surgery. In the STAR™ System, developed by VISX, Incorporated (Santa Clara, Calif.), a collimated laser beam used for photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) is delivered to the plane of surgery by means of an optical beam delivery system which provides both spatial and temporal integration for an excimer laser beam. In this system, a collimated laser beam is passed through a set of six prisms surrounding an open path to divide the incoming beam into seven beamlets. Further averaging in the temporal domain is performed by rotating the beam with a rotating telescope. The combination of beam splitting and rotation produces a laser beam having an intensity profile that may be used for refractive surgery. Such a system is described in U.S. Pat. Nos. 5,646,791 and 5,912,775, which are assigned to the assignee of the present invention and which are hereby incorporated fully by reference.
While highly effective in providing spatial and temporal integration to a collimated laser beam, this arrangement sometimes provides beamlets with minor non-uniformities, thus resulting in a laser beam having a slightly varied cross-sectional intensity profile at an ablation target. In other words, such an arrangement may provide less laser beam homogenization (or intensity profile averaging) than would be optimal. One solution would be to increase the number of prisms in the homogenization device, but such a device would be difficult to manufacture. Additionally, transmission of optics exposed to excimer lasers deteriorates with time, and this effect is especially large in relatively thick prism elements. Another disadvantage of a system as described in U.S. Pat. Nos. 5,646,791 and 5,912,775 is that alignment of the system can be relatively challenging.
Therefore, a need exists for improved laser beam homogenizing devices, systems and methods. Such devices, systems and methods would ideally provide for enhanced laser beam intensity averaging and homogenization, thus reducing or eliminating variations in intensity over a cross-section of a laser beam. Ideally, beamlets in such a system would be collimated. Also ideally, devices for homogenizing a laser beam would be relatively simple to produce, would provide for enhanced transmission of light and would be relatively resistant to wear and tear. At least some of these objectives will be met by the present invention.